Thallium halides


The thallium halides include monohalides, where thallium has oxidation state +1, trihalides in which thallium generally has oxidation state +3, and some intermediate halides containing thallium with mixed +1 and +3 oxidation states. These materials find use in specialized optical settings, such as focusing elements in research spectrophotometers. Compared to the more common zinc selenide-based optics, materials such as thallium bromoiodide enable transmission at longer wavelengths. In the infrared, this allows for measurements as low as 350 cm−1, whereas zinc selenide is opaque by 21.5 μm, and ZnSe optics are generally only usable to 650 cm−1.

Monohalides

The monohalides all contain thallium with oxidation state +1. Parallels can be drawn between the thallium halides and their corresponding silver salts, for example thallium chloride and bromide are light sensitive and thallium fluoride is more soluble in water than the chloride and bromide.
;Thallium fluoride
;Thallium chloride
;Thallium bromide
;Thallium iodide

Thallium(I) mixed halides

Thallium bromoiodide and thallium bromochloride are mixed salts of thallium that are used in spectroscopy as an optical material for transmission, refraction and focusing of infrared radiation. The materials were first grown by R. Koops in the laboratory of Olexander Smakula at the Carl Zeiss Optical Works, Jena in 1941. The red bromoiodide was coded KRS-5 and the colourless bromochloride, KRS-6 and this is how they are commonly known. The KRS prefix is an abbreviation of "Kristalle aus dem Schmelz-fluss", . The compositions of KRS-5 and KRS-6 approximate to and. KRS-5 is the most commonly used, its properties of being relatively insoluble in water and non-hygroscopic, make it an alternative to KBr, CsI and AgCl.

Trihalides

The thallium trihalides are less stable than their corresponding aluminium, gallium and indium counterparts and chemically quite distinct. The triiodide does not contain thallium with oxidation state +3 but is a thallium compound and contains the linear triiodide ion.
;Thallium fluoride
;Thallium chloride
;Thallium bromide
;Thallium triiodide

Mixed valence halides

As a group these are not well characterised. They contain both Tl and Tl, where the thallium atom is present as complex anions e.g. TlCl4−.

Halide complexes

;Thallium complexes
;Thallium fluoride complexes
;Thallium chloride complexes
;Thallium bromide complexes
;Thallium iodide complexes

Further information